Exhaust gas purifying system for vehicle

ABSTRACT

An exhaust gas purifying system for a vehicle may include a three-way catalyst into which an exhaust gas from an engine is introduced, an SCR catalyst positioned downstream from the three-way catalyst and reducing NO x , an oxidizing catalyst positioned downstream from the three-way catalyst, a rear oxygen sensor positioned behind the three-way catalyst and a controller receiving signals from the rear oxygen sensor and controlling a catalyst purge, where the controller ends the catalyst purge while the signals still show a lean state, after starting the catalyst purge following end of a fuel-cut.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2013-0158770, filed Dec. 18, 2013, the entire contents of which is incorporated herein by this reference for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purifying system for a vehicle, and more particularly, to an exhaust gas purifying system for a gasoline vehicle

2. Description of Related Art

Vehicles using gasoline as fuel are generally designed to remove HC, CO, and NO_(x), which are the main waste pollutants in exhaust gas of an engine, using a three-way catalyst. However, the three-way catalyst may purify all of the three main waste pollutants to a desired level only within λ-window, which is a very narrow range of an excess air ratio of about λ=1, such that control of the fuel-air ratio should be performed in order to ensure the performance of purifying the exhaust gas, which is difficult.

Together with the control of a fuel-air ratio, an oxygen storage matter such as ceria (CeO₂) is added to the three-way catalyst to allow storage of oxygen in the engine's lean combustion state and discharge the oxygen in the engine's rich combustion state. By doing so, the range of λ, which the three-way catalyst undergoes, is narrowed, substantially within λ-window, so that excellent purification efficiency of the three-way catalyst can be ensured.

Incidentally, if the traveling conditions allow, a vehicle is controlled to perform a fuel-cut in order to improve the fuel efficiency. At this time, fuel is not supplied to the engine, so that the three-way catalyst is in an oxygen-rich condition and the oxygen storage matter in the three-way catalyst stores a large amount of oxygen at this lean state.

Accordingly, even if the injection amount of fuel is close to λ=1, the three-way catalyst is in a lean state due to the large amount of oxygen stored by the oxygen storage matter after the fuel-cut, so that a large amount of NO_(x) is discharged.

In order to cope with the situation described above, catalyst purge is performed after the fuel-cut which controls a fuel-air ratio to be high, thus resulting in more supply of the fuel to remove the oxygen stored in the oxygen storage matter. However, the catalyst purge has an adverse influence on the fuel efficiency of the vehicles because more fuel is supplied and used.

Therefore, what is needed is an exhaust gas purifying system for a vehicle which can effectively purify noxious components in an engine's exhaust gas and can also contribute to improving fuel efficiency, which is a problem that prior art purifying systems do not address.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the present invention and should not be construed as an acknowledgment or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing an exhaust gas purifying system for a vehicle which can effectively purify noxious components in exhaust gas from an engine of a vehicle using gasoline as fuel, and can contribute to improving fuel efficiency of the vehicle.

An exhaust gas purifying system for a vehicle may include a three-way catalyst into which an exhaust gas from an engine is introduced, an SCR catalyst positioned downstream from the three-way catalyst and reducing NO_(x), an oxidizing catalyst disposed at downstream from the three-way catalyst, a rear oxygen sensor disposed behind the three-way catalyst, and a controller receiving signals from the rear oxygen sensor and controlling a catalyst purge, wherein the controller ends the catalyst purge while the signals still show a lean state after starting the catalyst purge following end of fuel-cut.

The exhaust gas purifying system for a vehicle may include an oxidizing catalyst which is positioned upstream of the SCR catalyst. Alternatively, the exhaust gas purifying system for the vehicle may include the oxidizing catalyst positioned downstream of the SCR catalyst.

A method of controlling an exhaust gas purifying system for a vehicle may include a purge start checking step of determining whether catalyst purge starts after a fuel-cut, a monitoring step of monitoring an output value of the rear oxygen sensor at downstream from the three-way catalyst to determine whether the output value shows a lean state after the catalyst purge starts, and a purge ending step of ending the catalyst purge while it is determined in the monitoring step that the output of the rear oxygen sensor shows the lean state. The purge ending step may include ending the catalyst purge when the output value of the rear oxygen sensor is close to being out of the lean state.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUVs), busses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, alternative fuel vehicles, (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exhaust gas purifying system for a vehicle according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating an exhaust gas purifying system for a vehicle according to an exemplary embodiment of the present invention; and

FIG. 3 is a flowchart illustrating a method of controlling an exhaust gas purifying system for a vehicle according to an exemplary embodiment of the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments which may be included within the spirit and scope of the invention as defined by the appended claims. Hereinafter, an exemplary embodiment of the present invention will be described with reference to the accompanying drawings so that those skilled in the Field of the Invention to which the present invention pertains may carry out the exemplary embodiment.

FIGS. 1 and 2, both illustrate exemplary embodiments of an exhaust gas purifying system for a vehicle of the present invention which may include a three-way catalyst 1 into which an exhaust gas from an engine is introduced; a selective catalytic reduction (SCR) catalyst 3 positioned downstream from the three-way catalyst 1 and reducing NO_(x); and an oxidizing catalyst 5 positioned downstream from the three-way catalyst 1.

The present invention may be configured such that the SCR catalyst 3 positioned downstream from the three-way catalyst 1 purifies NO_(x) discharged in a situation similar to that in which the three-way catalyst 1 operates in a lean combustion state of the engine due to oxygen stored in an oxygen storage matter after fuel-cut, using ammonia (NH₃) produced from the three-way catalyst.

Catalyst purge after the fuel-cut is for restoring the performance of the three-way catalyst 1 as soon as possible, but it is advantageous to end the catalyst purge early in view of fuel efficiency because fuel is additionally supplied during the catalyst purge. If the catalyst purge is ended early, the performance of the three-way catalyst 1 is not sufficiently restored, and NO_(x) or CO/HC is discharged, depending on how early the catalyst purge is ended. However, NO_(x) that is not processed by the three-way catalyst 1 due to the early end of the catalyst purge may be purified by the SCR catalyst 3, and CO and HC that are not processed by the three-way catalyst 1 may be purified by the oxidizing catalyst 5. Further, as the catalyst purge is ended early, fuel efficiency can be improved as well. NO_(x) is mainly discharged at a point in time in which the catalyst purge is ended is early, and CO and HC are mainly discharged, at a point in time in which the catalyst purge is ended is late.

In one aspect of the present invention as shown in FIG. 1, the oxidizing catalyst 5 is positioned upstream of the SCR catalyst 3, and in another aspect, the oxidizing catalyst 5 is disposed at downstream from the SCR catalyst 3. In this aspect the oxidizing catalyst 5 and the SCR catalyst 3 have only to be positioned downstream of the three-way catalyst 1.

A front oxygen sensor may be positioned ahead of the three-way catalyst 1, a rear oxygen sensor 7 may be positioned behind the three-way catalyst, and signals produced by these oxygen sensors may be provided to an ECU (ENGINE CONTROL UNIT), which is a controller, to make the ECU control the engine.

The ECU receives signals from the rear oxygen sensor 7 and may control the catalyst purge. In the present invention, the ECU ends the catalyst purge while the signals from the rear oxygen sensor 7 show still a lean state after starting the catalyst purge following end of fuel-cut.

That is, the ECU stops the catalyst purge not when the lean state has been changed to a rich state in view of the signals from the rear oxygen sensor 7 as prior art, but while the signals still show the lean state. The ‘lean state’ means that the signals from the rear oxygen sensor 7 still indicate a lean state, though a rich combustion has been performed in the engine by the catalyst purge.

FIG. 3 is a flowchart illustrating a method of controlling an exhaust gas purifying system for a vehicle according to an exemplary embodiment of the present invention which may include:

A purge start checking step S10 of determining whether catalyst purge starts after fuel-cut. The purge start checking step S10 may be configured to occur after a fuel-cut is stopped

A monitoring step S20 of monitoring an output value of a rear oxygen sensor 7 downstream from a three-way catalyst 1 to determine whether the output value shows a lean state after the catalyst purge starts.

A purge ending step S30 of ending the catalyst purge while it is determined in the monitoring step S20 that the output of the rear oxygen sensor 7 shows the lean state.

In one aspect of the present invention it is checked in the purge start checking step S10 that the catalyst purge has started, as described in the related art, after the fuel-cut is performed while a vehicle is traveling. The output value of the rear oxygen sensor 7 is continuously monitored in the monitoring step S20, the catalyst purge is forcibly ended while it is determined that the output value of the rear oxygen sensor 7 does not yet show the rich state, but shows the lean state, and NO_(x) discharged in this process is purified by the SCR catalyst 3 and small amounts of CO and HC are purified by the oxidizing catalyst 5.

The purge ending step S30 may be configured to end the catalyst purge when the output value of the rear oxygen sensor 7 is close to being out of the lean state. For example, in the case in which a standard output value of the rear oxygen sensor 7 is 450 mV and that an output value of 200 mV or less shows the lean state and an output value of 600 mV or more shows the rich state, the catalyst purge is ended when the output value approaches 200 mV. The catalyst purge may also be ended under 600 mV so that the amount of NO_(x) to be processed by the SCR is reduced and the three-way catalyst is more purged.

The aforementioned embodiments are only an example and the gist of the present invention is that although catalyst purge is determined based on the output value of the rear oxygen sensor 7 as described in the related art, the catalyst purge is not continued until it is determined that it is in the rich state, but is ended earlier as compared with the related art, and NO_(x) produced in this process is treated by the SCR catalyst 3 and small amounts of HC and CO are treated by the oxidizing catalyst 5.

As set forth above, according to certain exemplary embodiments of the present disclosure, noxious components in the exhaust gas from the engine of a vehicle using gasoline as fuel can be effectively purified, thus fuel efficiency of the vehicle can be improved.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for the purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. An exhaust gas purifying system for a vehicle, comprising: a three-way catalyst into which an exhaust gas from an engine is introduced; an SCR catalyst positioned downstream from the three-way catalyst and reducing NO_(x); an oxidizing catalyst positioned downstream from the three-way catalyst; a rear oxygen sensor positioned behind the three-way catalyst; and a controller receiving signals from the rear oxygen sensor and controlling a catalyst purge; wherein the controller ends the catalyst purge while the signals still show a lean state after starting the catalyst purge following end of a fuel-cut.
 2. The exhaust gas purifying system for a vehicle of claim 1, wherein the oxidizing catalyst is positioned upstream of the SCR catalyst.
 3. The exhaust gas purifying system for a vehicle of claim 1, wherein the oxidizing catalyst is positioned downstream of the SCR catalyst.
 4. A method of controlling the exhaust gas purifying system for a vehicle according to claim 1, the method comprising: a purge start checking step of determining whether catalyst purge starts after fuel-cut; a monitoring step of monitoring an output value of the rear oxygen sensor at downstream from the three-way catalyst to determine whether the output value shows a lean state after the catalyst purge starts; and a purge ending step of ending the catalyst purge while it is determined in the monitoring step that the output of the rear oxygen sensor shows the lean state.
 5. The method of claim 4, wherein the purge ending step includes ending the catalyst purge when the output value of the rear oxygen sensor is close to being out of the lean state. 